Osteoarthritis (0A) is characterized by the lack of retention of extracellular matrix components in articular cartilage. OA is likely manifested in part by the inability of the chondrocyte to retain matrix at the cell surface. CD44 is a transmembrane glycoprotein receptor that links the matrix to the chondrocyte, thereby controlling matrix assembly and retention It is hypothesized that phosphorylation of CD44 directly regulates CD44-mediated cell/matrix interactions, a process not yet fully understood. investigators have recently shown that casein kinase II alpha (CKIIalpha') phosphorylates the cytoplasmic domain of CD44 in human breast cancer cells. It is highly probable that CKII plays a critical role in cartilage metabolism via the same mechanism. We hypothesize that CKII functions in cartilage to indirectly regulate matrix assembly and retention by mediating CD44 phosphorylation. Aims set forth in this proposal include (1) determining the presence and distribution of CKII in chondrocytes in all zones of human articular cartilage. Immunohistochemistry and in situ hybridization will be conducted on cartilage explants or cultured chondrocytes derived from normal, damaged and OA tissue. Levels of CKII and CD44 expression will be compared using competitive RT-PCR and Western blot techniques. Experiments will then (2) determine the ability of CKII to mediate CD44 phosphorylation in cultured explants and chondrocytes. RT-PCR, immunoprecipitation/Western blot and particle exclusion techniques will assess the ability of CKII to regulate CD44 phosphorylation and subsequent pericellular matrix formation following CKIIalpha antisense oligonucleotide or matrix degrading enzyme treatment Finally, it will be (3) determined whether any of these parameters are altered following treatment with interleukin-1, a cartilage matrix degrading cytokine. Findings will establish the role of CKII in both normal and pathogenic cartilage.